Evaporation is a common technique used in modern analytical chemistry laboratories. It is frequently used to concentrate the end product of extraction operations for further analysis by techniques such as gas or liquid chromatography.
In environmental analysis, the volume of extract solvent that needs to be concentrated is usually large 200-500 ml. An evaporation method called Kuderna-Danish is used widely in this respect. However, this procedure has drawbacks: it is slow, recoveries of dissolved analytes in the concentrated fraction are poor, the glassware used is expensive and fragile, and the process is difficult to automate.
An improved technique for evaporating solvent for analyte concentration is found in Friswell, U.S. Pat. No. 4,707,452. Using this method a stream of gas is directed in a helical path down the inside wall of an open evaporation vessel seated in a temperature controlled bath. This method provides a more efficient solvent evaporation, thus allowing for the use of lower bath temperatures to prevent the degradation of temperature-labile analytes dissolved in the solvent inside the evaporation vessel. However, the Friswell system does exhibit certain disadvantages. First, a large amount of gas is required to accomplish evaporation. Inert gases such as argon or nitrogen are commonly used for this purpose, and although readily available, they are expensive in the preferred highly pure form. Second, the vapors from the solvents evaporated, typically organic solvents like chloroform and hexane, are toxic. Good laboratory practice mandates that evaporated solvent vapors be removed by standard laboratory ventilation hood systems. Current federal and state environmental regulations govern the release of small amounts of these vapors in this way, but larger amounts can cause problems for laboratories. Third, the purified solvents evaporated are costly and recovery of the evaporated solvent for recycling would be desirable.
The object of this invention, therefore, is to provide an improved evaporation apparatus which provides for solvent recovery.